Raise error on unknown primary key.

If we don't have a primary key when we ask for it, it's better to fail
fast. Fixes GH #2307.

1 files changed, 14 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index ad7d8cd63c..8262b60f6e 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -169,4 +169,18 @@ module ActiveRecord
       @errors = errors
     end
   end
+
+  # Raised when a model attempts to fetch its primary key from the database, but the table
+  # has no primary key declared.
+  class UnknownPrimaryKey < ActiveRecordError
+    attr_reader :model
+
+    def initialize(model)
+      @model = model
+    end
+
+    def message
+      "Unknown primary key for table #{model.table_name} in model #{model}."
+    end
+  end
 end